A number of intra-vaginal devices have been described in our U.S. Pat. No. 3,811,423. Such devices function as anchor assemblies including a number of spring-like strands each in a hoop configuration mounted at opposite ends to mounting rings. Such devices may include a cervical clamping ring. Other similar devices are described in British Pat. No. 1,384,254. Such devices are constructed to prevent simultaneous expulsion thereof by the animal. Although the devices are highly effective for retention in the vaginal lumens of animals such as pigs and cows post-parturition when the vaginal linings of such animals have been distended, they are not as effective for retention in pre-parturition animals.
Many intra-uterine devices have been developed for the purpose of contraception. However, retention of such devices in the uterus is substantially less difficult than retention in the vagina. Retention in the uterus is facilitated by the cervix, located at the uterus entrance, a tightly closed passageway which effectively blocks expulsion of the device. In contrast, the vaginal lining of an animal such as the cow includes a sphincter-like muscle. However, it does not provide a normally tightly closed constriction such as the cervix. Also, the animal's vagina tends to eject foreign bodies. Because of such distinctions, devices retained for long periods of time in the uterus may not be effective for retention in the vagina.
One intra-uterine contraception device is set forth in British Pat. No. 1,129,712. In the embodiment of FIGS. 1-5, a number of thin filaments (cross-section of 1.5 mm) project from an elliptical loop. These soft, pliable, thin filaments have little structural strength. The patent states at page 2, lines 98-103, that rounded corners at the filament ends which could constitute projections should be avoided. There is no suggestion that such a device be adaptable for retention in an animal's vagina. Assuming there were such a suggestion, a device of the indicated type would not be effective for that purpose.